Digital watermarking is a technology which allows undetectable information to be hidden in an electronic file. The presence of the watermark is not apparent to a user and generally does not negatively affect the electronic file to which it is added. The watermark information is typically used to identify the originator of the electronic file, but can be used for other purposes, such as to confirm a legitimate user of the electronic file, to determine whether certain content has been aired or played, or many other uses.
Digital audio watermarking conceals a watermark in a digital audio file. In many instances, the digital audio file is a discrete audio file. In some instances, digital audio watermarks are being used by entities in the television transmission area to provide revenue outside of agreements between broadcasters and television networks or studios. Many times, a broadcaster or television network would like to know whether content supplied by such an entity contains an audio watermark and to prevent detection of an audio watermark by a third party device.
There are a number of different methodologies available to conceal an audio watermark in an audio file. Some of these methodologies include direct current (DC) watermarking, phase encoding, spread spectrum watermarking and echo watermarking. Direct current (DC) watermarking involves concealing the watermark data in lower frequency components of an audio signal. The lower frequency components are below the threshold of human perception.
Phase encoding conceals the watermark data by encoding the watermark data in an artificial phase signal. Spread spectrum watermarking uses direct sequence spread spectrum (DSSS) to spread the watermark data signal over the entire audible frequency spectrum such that it approximates white noise. Echo watermarking conceals watermark data by distorting an audio signal in a way that causes the human auditory system to perceive the watermarked audio file as environmental distortion. Spread spectrum watermarking is one of the more widely used digital audio watermarking techniques.
These watermarking methodologies generally require complex systems to implement and detect. Therefore, there is a need for a way of efficiently and easily preventing audio watermark detection.